1. The Field of the Invention
The present invention relates generally to piezoelectric motors. More particularly, the present invention relates to a piezoelectric motor having a mesh electrode, a partial electrode interface, and a pair of coil springs.
2. The Background Art
Accurate micro-positioning and actuation are often required in certain applications, such as slide positioning systems. Piezoelectric drivers have been utilized to replace leadscrews and gears typically used in such slide positioning systems. The piezoelectric drivers use a piezoelectric material to convert an electrical field applied to the piezoelectric material to mechanical displacement, or a dimensional change in the piezoelectric material. Thus, the piezoelectric material may be affixed to a first member, such as the base of a slide, and engage or bear against a second member, such as the platform of the slide. The piezoelectric material may be oriented such that the dimensional change, or expansion and contraction, of the piezoelectric material due to the applied electrical field causes the second member to move with respect to the first member.
One such example of a piezoelectric motor is disclosed in U.S. Pat. No. 4,622,483, issued Nov. 11, 1986, to Staufenberg, Jr. et al. Staufenberg, Jr. et al. discloses a pair of engaging elements which selectively clamp and translate a housing relative to a separate member. A pair of piezoelectric driving elements are each coupled to one of the engaging elements. The piezoelectric driving elements selectively expand and contract in response to an applied voltage of selected magnitude and frequency. Thus, the piezoelectric driving elements produce a variable driving force between the housing and the engaging elements, and which is conducted through the engaging elements to apply a variable clamping force to the separate member. The engaging elements are responsive to the expansion and contraction of the piezoelectric driving elements to selectively inhibit and impart relative motion between the housing and the separate member to produce motion.
Some advantages of piezoelectric motors include precise positioning (i.e. nanometer precision), efficiency, lack of backlash, and quiet operation. Despite the advantages realized by the Staufenberg, Jr. et al. motor, several disadvantages exist with such piezoelectric motors, and other commercially available motors. One disadvantage is inconsistent performance between similar motors, and individual motors. Actual motors tend to be loose, resulting in inefficient performance, inconsistent performance, and premature failure.
Another disadvantage is difficulty in manufacturing the motors. Piezoelectric motors often must be individually hand made. Thus, the manufacturing process is labor intensive and expensive. In addition, it is difficult to produce large quantities because each motor is hand made. Furthermore, it is difficult to control the manufacturing process.
Another disadvantage is tight tolerances are required. As stated above, actual motors tend to be loose, resulting in inefficient performance, inconsistent performance, and premature failure.
Another disadvantage is short life and high wear of the motors. For example, attachments between various components fail. In addition, contact points tend to wear quickly and unevenly.
It has been recognized that it would be advantageous to develop a piezoelectric motor with consistent performance for the motor itself, and consistent performance between similar motors. It would also be advantageous to develop such a motor which is more efficient, and has better performance. It would also be advantageous to develop such a motor with a longer life, and better wear characteristics. It would also be advantageous to develop such a motor which is easier and less expensive to manufacture, and which lends itself to a less labor intensive process.
The invention provides a piezoelectric motor for driving a separate member. Such a motor may be utilized for a slide having a base and a platform movably disposed on the base. The motor of the present invention may be fixed to the base of the slide, while the separate member is fixed to the platform of the base, such that the motor moves the platform on the base.
An exemplary motor includes a head to movably engage the separate member, and one or more piezoelectric blocks coupled to the head. The piezoelectric blocks selectively expand and contract in response to an applied electric field to displace the head and the separate member. An electrode extends between the head and the piezoelectric blocks to apply the electric field. In a more detailed example, the motor includes a housing fixed with respect to the separate member, and a mounting block movably connected to the housing and affixed to the piezoelectric block.
In accordance with one aspect of the present invention, one or more apertures may be formed in the electrode to create one or more spaces between the head and the piezoelectric block. An adhesive may be disposed in the spaces of the electrode between the head and the piezoelectric block to join the head and the piezoelectric block. The electrode forms a rigid structure between the piezoelectric motor and head to displace as the piezoelectric block expands and contracts, and to transfer the expansion and contraction of the piezoelectric block to the head. The electrode may include a mesh material with a plurality of openings.
In accordance with another aspect of the present invention, an interface or joint is formed between the head and the piezoelectric block which includes at least two zones, including: a first rigid zone and a second compliant zone. The electrode may extend through only a portion of the interface, forming the rigid zone. An adhesive may be disposed between another portion of the interface, forming the compliant zone. The compliant portion of one joint may comply as the other piezoelectric block expands and contracts.
In accordance with another aspect of the present invention, a pre-load mechanism may be disposed between the housing and the mounting block to apply a force to the mounting block, piezoelectric block, and head, in a linear direction oriented perpendicular to the separate member, to force the head against the separate member. The pre-load mechanism may be a pair of coiled springs on opposite sides of the head.
Additional features and advantages of the invention will be set forth in the detailed description which follows, taken in conjunction with the accompanying drawing, which together illustrate by way of example, the features of the invention.